RUUD van Nistelrooy's four-goal haul against Sparta Prague has only underlined his huge importance to Manchester United - and when his fortunes rise and dip, so too, do his team's.

The Dutch striker is on something of a rollercoaster ride. He scored the crucial penalty against Arsenal, then found himself suspended for three games for that ugly challenge on Ashley Cole.

Van Nistelrooy's absence appeared chasm-like in the 2-0 defeat by Portsmouth last weekend but he returned as a conquering hero in the Champions League.

Now United will be without him again for Sunday's derby and skipper Roy Keane is only too aware there is a void to be filled.

Keane said: "Do the four goals illustrate his importance to us? Yes, we all know that it's a team game, but Ruud's record speaks for itself. He's an out-and-out goalscorer. Give him four chances, he scores four goals, not a bad percentage.

"There's not a lot of Ruuds about and we do miss him when he's not playing."

Keane emphasised that it was up to all the team, not just the strikers, to make up for van Nistelrooy's absence.